1. Field of the Disclosure
The technology of this disclosure relates to distributed antenna systems (DASs), such as distributed communications systems, which are capable of distributing wireless radio frequency (RF) communications services over wired communications media.
2. Technical Background
Wireless communications have ever-increasing demands for high-speed mobile data communications. As an example, so-called “wireless fidelity,” or “WiFi” systems and wireless local area networks (WLANs). Wireless communications systems communicate with wireless devices known as “clients,” which reside within a wireless range or “cell coverage area” in order to communicate with an access point device.
One approach to deploying a wireless communications system involves the use of “picocells.” Picocells are RF coverage areas having a radius in a range from a few meters up to approximately twenty (20) meters. Picocells can be utilized to provide a number of different services (e.g., WLAN, voice, radio frequency identification (RFID) tracking, temperature and/or light control, etc.). Because a picocell covers a small area, there are typically only a few users (clients) per picocell. Picocells also allow for selective wireless coverage in small regions that otherwise would have poor signal strength when covered by larger cells created by conventional base stations.
In conventional wireless systems as illustrated in FIG. 1, coverage areas 10 in a DAS 12 are created by and centered on remote units 14 connected to a head-end equipment 16 (e.g., a head-end controller, a head-end unit, or a central unit). The remote units 14 receive wireless communications services from the head-end equipment 16 over a communications medium 18 to be distributed in a respective coverage area 10. The remote units 14 include information processing electronics, an RF transmitter/receiver, and an antenna 20 operably connected to the RF transmitter/receiver to wirelessly distribute the wireless communications services to wireless client devices 22 within the coverage area 10. The size of a given coverage area 10 is determined by the amount of RF power transmitted by the remote unit 14, receiver sensitivity, antenna gain, and RF environment, as well as by the RF transmitter/receiver sensitivity of the wireless client device 22. Wireless client devices 22 usually have a fixed RF receiver sensitivity, so that the properties of the remote unit 14 mainly determine the size of the coverage area 10.
In wireless/cellular networks, such as the DAS 12 in FIG. 1, high power equipment used for distributing signals over long distances consumes significant energy. Each remote unit 14 includes an electronic unit that consumes energy for operation in receiving and transmitting wireless communications signals. For example, in some conventional DASs, remote units 14 can consume about fifteen watts (15 W) for each wireless service provided. In some conventional DASs, three or more services may be provided simultaneously, resulting in power consumption of forty-five watts (45 W) or more for each remote unit 14. Many conventional DASs include more than fifty (50) remote units 14, with some systems including one hundred (100) remote units 14 or more. Thus, total power consumption in these systems can exceed 1.5 or 3 kilowatts (kW).
High power consumption in the remote units 14 also generates heat that may require dissipation to avoid damaging components in the remote units 14, and to avoid interfering with the climate control preferences in the environment of the distributed antenna system 12 (e.g., enclosed in a building). This excess heat is typically dissipated by a building's air-conditioning system, which increases operating costs. In addition, conventional DASs 12 are usually operated at all times in order to maintain coverage throughout the building, including hours and/or days during which there is little activity in the coverage areas 10. Thus, the high power consumption experienced by these conventional DASs 12 is continuous, which further adds to operating costs.